| Message ID | 3800eaa8-a4da-b2f0-da31-6627176cb92e@physik.fu-berlin.de |
|---|---|
| State | New |
| Headers | show |
| Series | Calculating array sizes in C - was: Re: Build regressions/improvements in v6.2-rc1 | expand |
Isn't this supposed to be caught by this check: >>> >>> a, __same_type(a, NULL) >>> >>> ? >> >> Yeah, but gcc thinks it is smarter than us... >> Probably it drops the test, assuming UB cannot happen. > Hmm, sounds like a GGC bug to me then. Not sure how to fix this then. I don't see a clear bug at this point. We are talking about the C expression __same_type((void*)0, (void*)0)? 0 : sizeof((void*)0)/sizeof(*((void*0)) This expression is valid (assuming __same_type works, which is a GCC extension), and should return 0. As of now, I have no indication that this expression does not return 0. Also, it is true that this expression contains the suspicious pattern "sizeof(void*)/sizeof(void)", which is does not calculate the size of any array. GCC is free to emit as much warnings is it wants for any kind of expressions. From a C standard point of view, it's just a "quality of implementation" issue, and an implementation that emits useless warnings is of low quality, but not non-conforming. In this case, we requested that gcc refuses to compile if it emits any kind of warning, which instructs gcc to reject programs that would be valid according to the C standard, but are deemed to be "likely incorrect". I suggest to file a bug against gcc complaining about a "spurious warning", and using "-Werror -Wno-error-sizeof-pointer-div" until gcc is adapted to not emit the warning about the pointer division if the result is not used. Regards, Michael Karcher
Hello!
> Can someone please file a GCC PR? With reduced testcase preferably.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108483
There you are.
Kind regars,
Michael Karcher
Hello Adrian, > Could you post a kernel patch for that? I would be happy to test it on my > SH-7785CLR board. Also, I'm going to file a bug report against GCC. I filed the bug already. It's https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108483. The diff is attached. It's published as CC0 in case anyone considers this trivial change copyrightable. This patch prevents this one specific warning from being upgraded to "error" even if you configure the kernel to use "-Werror". It still keeps it active as warning, though. Kind regards, Michael Karcher diff --git a/Makefile b/Makefile index e09fe100efb2..b4cd075c6a19 100644 --- a/Makefile +++ b/Makefile @@ -870,7 +870,7 @@ stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG) := -fstack-protector-strong KBUILD_CFLAGS += $(stackp-flags-y) -KBUILD_CPPFLAGS-$(CONFIG_WERROR) += -Werror +KBUILD_CPPFLAGS-$(CONFIG_WERROR) += -Werror -Wno-error=sizeof-pointer-div KBUILD_CPPFLAGS += $(KBUILD_CPPFLAGS-y) KBUILD_CFLAGS-$(CONFIG_CC_NO_ARRAY_BOUNDS) += -Wno-array-bounds
Hi! On 1/20/23 20:29, Michael Karcher wrote: > Hello Adrian, >> Could you post a kernel patch for that? I would be happy to test it on my >> SH-7785CLR board. Also, I'm going to file a bug report against GCC. > > I filed the bug already. It's https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108483. > > The diff is attached. It's published as CC0 in case anyone considers this trivial change copyrightable. This patch prevents this one specific warning from being upgraded to "error" even if you configure the kernel to use "-Werror". It still keeps it active as warning, though. I used the following variant and it fixes the issue for me: diff --git a/arch/sh/Makefile b/arch/sh/Makefile index 5c8776482530..11b22f7167d2 100644 --- a/arch/sh/Makefile +++ b/arch/sh/Makefile @@ -167,7 +167,7 @@ drivers-y += arch/sh/drivers/ cflags-y += $(foreach d, $(cpuincdir-y), -I $(srctree)/arch/sh/include/$(d)) \ $(foreach d, $(machdir-y), -I $(srctree)/arch/sh/include/$(d)) -KBUILD_CFLAGS += -pipe $(cflags-y) +KBUILD_CFLAGS += -pipe -Wno-error=sizeof-pointer-div $(cflags-y) KBUILD_CPPFLAGS += $(cflags-y) KBUILD_AFLAGS += $(cflags-y) If you agree, can you post a patch to LKML so we can unbreak the SH build for CONFIG_WERROR? Thanks, Adrian
diff --git a/include/linux/sh_intc.h b/include/linux/sh_intc.h index c255273b0281..07a187686a84 100644 --- a/include/linux/sh_intc.h +++ b/include/linux/sh_intc.h @@ -97,14 +97,12 @@ struct intc_hw_desc { unsigned int nr_subgroups; }; -#define _INTC_ARRAY(a) a, __same_type(a, NULL) ? 0 : sizeof(a)/sizeof(*a) - #define INTC_HW_DESC(vectors, groups, mask_regs, \ prio_regs, sense_regs, ack_regs) \ { \ - _INTC_ARRAY(vectors), _INTC_ARRAY(groups), \ - _INTC_ARRAY(mask_regs), _INTC_ARRAY(prio_regs), \ - _INTC_ARRAY(sense_regs), _INTC_ARRAY(ack_regs), \ + ARRAY_SIZE(vectors), ARRAY_SIZE(groups), \ + ARRAY_SIZE(mask_regs), ARRAY_SIZE(prio_regs), \ + ARRAY_SIZE(sense_regs), ARRAY_SIZE(ack_regs), \ } struct intc_desc {